It is important in a number of situations to be able accurately to analyse the exhaled breath of a test subject. The most common reason for doing this is to detect the presence of alcohol in the test subject's breath, which will of course be indicative of the test subject having a raised blood-alcohol level and thus impaired judgment and reaction times. Testing for alcohol in this way is very important for safety reasons in a large number of situations including, for example, the operation of heavy or dangerous machinery, the operation of aircraft, and the operation of motor vehicles. Breath testing for alcohol is now widely used in the area of law enforcement and is routinely carried out on motor vehicle drivers on the road networks of most major countries, with strict penalties in place for drivers found to be driving under the influence of alcohol.
Alcohol is a major factor in a very large number of road accidents, and so great efforts are made to reduce the incidence of driving under the influence of alcohol. One proposal which is now being considered more widely is the provision of so-called “alco-locks” in motor vehicles which will prevent operation of the motor vehicle until an approved breath sample has been given by the driver having an alcohol content below a predetermined maximum threshold. It is envisaged that the device of the present invention will be particularly useful in such alco-lock arrangements. However, it is to be appreciated that the invention is not limited to use in alco-lock arrangements, and could find wider application in the field of alcohol breath testing. The device of the present invention could be more widely employed in breath analysis more generally, and may not even be restricted to testing for the presence of alcohol. Nevertheless, the present invention is described herein with specific reference to alcohol testing.
Whilst alcohol testing for evidentiary of diagnostic purposes is generally achieved by infrared spectroscopy which is very accurate, a simpler method of alcohol testing is normally used for screening purposes; for example at the roadside by law enforcement personnel, or in the case of alco-locks installed in vehicles. Alcohol testing for screening purposes has therefore previously been achieved via catalysis; for example using fuel cells or semiconductor devices. These types of device are advantageous in terms of production cost, but have been found to suffer from problems of unreliability. The catalytic function is difficult to control, and the sensors have a limited lifetime. Furthermore, devices of this type require a test subject to deliver forced expiration into a tight-fitting mouthpiece which can be problematic for people with impaired respiratory function, and will generally be inconvenient and off-putting for drivers in the case of vehicle alco-locks.
It has therefore been proposed to provide improved breath analyser devices that do not require physical contact between the device and the test subject. This type of device is particularly advantageous in the case of alco-locks because it can be conveniently positioned on the dashboard, steering wheel, or A-pillar of a motor vehicle for receipt of a breath sample from a driver test subject in a normal, or reasonably normal, driving position. However, testing in this manner will of course mean that the breath sample is diluted with ambient air.
US2013/0231871 A1 proposes a type of no-contact breath analyser device which address the issue of ambient air dilution of the breath sample by measuring the concentration of a tracer substance such as carbon dioxide within the sample in order to estimate the degree of dilution and thereby allow the estimation of the true breath concentration of alcohol. Whilst this type of device has some very significant benefits, it has been found that accuracy problems can occur when gas entering the device is cold. One problem which arises is that the cold gas can cause condensation to be formed inside the sensing region of the device which can disrupt the operation of the sensors inside the device. However, it has also been found that simply the low temperature of the inlet gas can also disrupt the sensors.
There is therefore a need to address these problems, which it is to be noted are not exclusive to the type of device proposed in US2013/023181 A1, and can also arise in other types of breath analyser device.
It is an object of the present invention to provide an improved breath analyser device.